In general, a shock absorber attached to a suspension system of an automobile is arranged as follows. A piston connected with a piston rod is slidably fitted in a cylinder having a hydraulic fluid sealed therein, and a flow of hydraulic fluid induced by sliding movement of the piston in the cylinder in response to the stroke of the piston rod is controlled by a damping force generating mechanism comprising an orifice, a disk valve, etc., thereby generating a damping force.
In this type of shock absorber, the valve opening characteristics of the disk valve and the flow path area of the orifice are determined so as to set optimal damping force characteristics from the viewpoint of ride quality and steering stability of the vehicle. In a shock absorber disclosed in Patent Literature 1, for example, a sub-valve functioning as a check valve is incorporated in a disk valve comprising a stack of a plurality of disks, thereby increasing the degree of freedom for setting clamping force characteristics and thus obtaining optimal damping force characteristics.